Some biochemical aspects of chick embryo retina differentiation were studied: 1) An alternative route for GABA synthesis was characterized in the retina; which depends upon the conversion of putrescine to GABA. 2) Glutamic acid decarboxylase specific activity in the retina, increased during the course of embryonic development, either when measured in ovo or in aggregate cultures. 3) The presence of GABA in the culture medium prevented the development of glutamic acid decarboxylase activity in aggregate cultures. 4) The proposed course of this project is to attempt to correlate the biochemical changes observed, with synaptogenesis in the retina.